Maintenance of skin moisturization is a major problem in the cosmetics industry, which is in search of moisturizing cosmetic agents that can be used in any type of cosmetic composition, and also new targets on which these active agents can act, especially to limit the evaporation of water or to improve the transportation of water in the epidermis.
Aquaporins (AQPs) are a family of transmembrane proteins which form channels that facilitate the diffusion of water and small molecules, such as glycerol and urea, in solution.
To date, 13 proteins of this family have been identified in man (numbered from AQP0 to AQP12). They are widely distributed in the body and most particularly in organs that are the site of considerable movement of water between different compartments, such as the kidneys (water reabsorption) or the skin (transepidermal water loss).
Certain aquaporins known as aquaglyceroporins, for instance AQP3 and AQP9, also show permeability to small solutes such as glycerol, urea, purines and pyrimidines, which also play an important role in maintaining the level of hydration of tissues.
AQP-3, revealed in the plasma membrane of human epidermal keratinocytes, is distributed throughout all live epidermis (R Sougrat et al. JID 2003, 118 : 678-685).
AQP9 has more recently been revealed in these same epidermal cells, but more locally in the upper (superficial) layers of the human epidermis (J M Verbavatz et al., Expression of aquaporin 9 and 10 in human keratinocytes during differentiation, 5th International Conference on Aquaporins, Nara Japan, July 2007).
This localization of AQP9 in the outermost layers of the skin, which are the ones that are the most exposed to dehydration, makes AQP9 a biological target of choice for improving the surface moisturization of the skin.
FR 2 801 504 discloses an extract of Ajuga turkestanica as an agent for stimulating the expression of AQP3 and its cosmetic use as a moisturizer.
WO 2007/007 255 discloses various agents for stimulating the expression of aquaporins AQP3 and AQP9 in the skin, and also their cosmetic use.
Common mallow (Malva sylvestris), also known as wild mallow or wood mallow, is a biennial herbaceous plant of the Malvacea family. The use of extracts of this plant in cosmetics is known.
FR 2 814 070 discloses a process for preparing an aqueous extract of leaves of the plant species Malva sylvestris, and the use of the said extract as an anti-ageing cosmetic agent in cosmetic compositions.
No document thus discloses the moisturizing properties of an extract of mallow (Malva sylvestris) via stimulation of the expression of AQP9 in epidermal cells.
This property makes the use of such an extract particularly advantageous in cosmetic compositions, for performing care via which it is sought to maintain or to promote the moisturization of the skin.